The proposed research focuses on the development of a compact, high-field (HF) Electron Paramagnetic Resonance (EPR) spectrometer for DNP-enhanced solid-state, magic-angle-spinning (MAS) NMR spectroscopy. The spectrometer will allow researchers to record the EPR spectra and obtain valuable relaxation parameters of the DNP sample under the same conditions under which the DNP experiment is performed. This data is critical for choosing the best polarizing agents and sample preparations for maximizing DNP sensitivity. In recent years, DNP has proven to be a robust method for increasing signal intensities in NMR experiments in laboratories around the world, and substantial progress has been made in adapting DNP for solid-state NMR spectroscopy. To understand and optimize the DNP process, it is crucial to fully understand the EPR spectrum and relaxation parameters of the polarizing agent. However, less than a dozen academic groups have succeeded in building the high-field spectrometer required to measure them, leaving researchers with little more than an educated guess regarding their sample's EPR properties. . We propose to market an affordable, compact EPR spectrometer that can easily be adapted to cover the complete frequency range currently used in DNP spectroscopy. The system can either be added to already existing gyrotron-based DNP system or allows the upgrade of an existing NMR spectrometer to do DNP spectroscopy. The spectrometer will be compact and turnkey so that the system can also be used by non- experts. During this project we will move the 263 GHz prototype EPR spectrometer to a 1st generation product and design and fabricate components that are required to retrofit existing NMR spectrometers and demonstrate their performance on a 400 MHz DNP-NMR spectrometer at a collaborator's site. With this technology, researchers can accurately determine EPR characteristics so they can develop new, optimized polarizing agents, maximize DNP sensitivity, and accelerate their research. This will be of large interest to many projects funded by the U.S. National Institutes of Health.